James, I've read your recommendations on using 1" of 6# insulating blanket. I'm building a 36" igloo style oven and will finish up the oven brickwork this coming w/e. Based on the rec's, next comes the 1" blanket, then 4" of perlcrete. I'll try to post some pics shortly...

Can I skip the blanket? If I were to skip the blanket, do I need a slip plane between the oven and the perlcrete? Is 5" or 6" of perlcrete enough to compensate for omitting the blanket? :confused: Anyone else got an opinion/experience to add?

btw, for anyone just getting started, harbor freight (www.harborfreight.com) has a 10" brick/tile wetsaw on sale for $199. It's not a name brand but for the money... :cool:

Thanks for all the help!

james

12-15-2005 11:10 AM

It's intereesting that there are two reasons to insulate something -- either to keep heat in, where you want it, or to keep it from getting to somewhere that you don't want it. The first is the logic behind using an insulating blanket. It is more efficient than vermiculite/perlite, so it does a good job of keeping heat inside the oven. The other reason to consider using it is to provide a solid layer that will help keep loose insulation from ever working its way into the oven through a crack or seam. A blanket does cost a little more than buying the extra couple bags of vermiculite.

2" of loose insulation is close to 1" of woven ceramic blanket, so if you go to 5"-6" loose, you won't get heat on your enclosure walls.

You don't have to worry about a slip plane -- vermiculite loose or casted with portland cement isn't solid enough for that to matter.

Hope this is helpful.
James

DavidK

12-15-2005 12:57 PM

Thanks James. Your guidance is always helpful! :D Since my oven will be finished as an igloo, it will have a cast insulating shell with the final layer being stucco. So as I read it, a 6" layer is equal to 4" perlcrete + 1" blanket.

As for the blanket, Thermal Products is charging $1/sf or $49.50/box, so based on my calculations, I only need about 24sf. Add shipping and we're talking $30-ish. That's more than reasonable as far as ROI, but for me, it isn't the cost but a burning desire to steam ahead without being slowed by a 7-10 day UPS delivery... Decisions, decisions.

btw, Thermal Products is only carrying #8 1"x24" insulfrax now, but the price seems more than reasonable...